115 Opti

[dabalone]

Have a new 115 Optimax on a 17'4' tracker, right now with the stock alum prop I can get 5000 rpm with motor trimmed up some. Motor is rated at up to 5750 rpm's, how important is it to stay close to those peak rpm's for the motor? I have installed smart tabs to help with the porpoising and chine walk and they really work well. When starting at hole shot the boat jumps on plane quickly but it sounds like substantial slippage when I nail it. If needed should I be looking to pick up rpm's with a new prop or some other means like raising the motor?

Thanks

 

[even125]

Re: 115 Opti

You are a mess! I am no guru but I muddle my way through.

Do this, tie those tabs into their up position, raise the engine 2 holes and go for a run IF the prop doesn't ventilate too badly and if it does go down 1 hole.

You will now have a boat that reacts to trim, pops onto the plane easier, stays on the plane at lower RPMs, has a higher WOT and best of all your porpoising will be at least decreased or GONE!.

Then after you have this new boat do runs and record to calculate your total slip, then use this data as you are now at or near ready to choose a new prop that will take you further yet again.

Of coarse I am assuming that whoever proped your rig did just as bad a job with motor height, there is a chance also that the prop is so far out but the height is OK but I would assume both are in need of fixing unless more informed on your particular setup.
cheers even125

 

[dabalone]

Re: 115 Opti

Thanks for the reply and advice. The motor is at the lowest mounting holes and seems really low, I cannot tell where the cavitation plate is in relation to bottom of hull because the trailer is so low I cannot lower the motor near an upright position. So if I go ahead and raise the motor up and test it, am I making sure the prop does not cavitate with the motor vertical and no trim? I need to find what size and pitch my prop is to post that info. It is the stock prop that came with the motor.

 

[even125]

Re: 115 Opti

Hi again my recipe is a working mans recipe -more effort low overall cost in relative terms.

Any possibility of pushing the boat a bit further back on the trailer, just enough that the engine can be lowered to vertical? if so take the opportunity to raise the engine while you are it, it can be 15minute exercise for one person.

Here is one way to do it, I assume you have some form of adjustable jockey wheel on the front of your trailer or at least a jack.

With the engine vertical place bricks, wood whatever you have (even the concrete floor) under the leg fin (skeg) use the jockey wheel to lower and raise the back of the boat until the fin is supporting the engines weight, then loosen the two slide engine mount bolts a couple of turns til the washers have a bit of slop now remove totally the two captive hole mount bolts (you may need to fine tune the height of the trailer rear at this point), then spray a lubricant around the slide bolts to lessen any possible paint damage due to sliding.

Now lower the rear of the trailer with the jockey wheel until the two captive bolt holes line up at your chosen higher setting, refit bolts, torque them all up and you are ready to go.

Sorry long winded I know, pretty soon I will run out of knowledge on your particular boat, when all the generic setup stuff is out of the way, hope someone can chime in with the higher tier side of getting it tuned for best performance if that is where you plan to go.

Honestly it is not impossible to gain an extra 600rpm with just an engine height raise, I did it just this week as the 5000rpm WOT and therefore associated speed it was running at was too slow to get the hull to lift and further reduce overall drag, after the engine lift the boat felt turbo charged above 5000rpm to 5600 as rpm rose in concert with decreasing prop slip till it all maxed out, I can go a hole higher yet again on this boat!

hope you have the same experience.


cheers even125

 

[even125]

Re: 115 Opti

In relation to your ventilation question, the bottom line for you at this point is to go with what you can get away with, I assume ATM you are not seeing true ventilation but actually slippage and the motor bogging down a bit when you gun it, a total assumption on my part.

Regardless if motor height is too low (another assumption) therefore ventilation should be less of an issue in theory compared to a higher tuned setup.

When you take off always start with max -ve trim (leg tucked under) from here you will quickly learn what suits your style and the package the best.

cheers even125

 

[dabalone]

Re: 115 Opti

Thank you even, ok first step for me is to raise the motor a couple holes and try it out. Once I do that the prop questions will come next. Thanks again, I will post my results as I go along.

Dab

 

[even125]

Re: 115 Opti

Hi Again opti, when you do get around to eyeballing the realation of your vent plate to hull bottom if it happens to be around 1/2 inch or above the bottom you will be at crossroads re minor extra height or new prop.
Because raising or lowering the engine is such a fast and simple affair it is IMO very much worth getting to know what each setting gives you good or bad, but be mindfull of too high at speed with cooling.

Because of your other symptoms I make the assumption it is too low ATM but it may not be, best case is too low because raising the engine in my experience makes a big positive difference to those symptoms and is cheap to do.

Best of luck and look forward to hearing whatever you attempt, don't forget to write down the RPM reached with the top speed by GPS at the engine height each test so you can throw some structured questions on this forum and get good answers for tuning it properly.

cheers even125